Method of welding edges of glass sheets

ABSTRACT

Marginal edge portions of a pair of glass sheets are welded together to make a multiple glazed unit by sequentially imposing a voltage on marginal edge portions of a sheet followed by alternately imposing a voltage on opposed corners of the sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for welding glasssheets together to make a multiple glazed unit.

2. Discussion of the Prior Art

In the manufacture of double glazed window units, it is well known thatsuch units can be made by uniting the margins of an assembly of glasssheets with a continuous peripheral weld, the central regions of thesheets which are bound by the continuous weld being pulled apart whilethe welding periphery is soft to establish a desired spacing between thesheets. In the process of manufacturing such all-glass multiple glazedunits, two glass sheets are first carefully washed, dried, preheated andassembled at a welding station one above the other. An electricallyconductive stripe is deposited on one of the sheets, generally on theupper surface of the upper glass sheet, to form a continuous peripheralelectrical path. A plurality of electrodes, preferably placed at thecorners of a rectangular window unit, are provided to direct the flow ofelectrical heating currents through selected portions of the stripecausing it to be heated. The portions of the upper sheet underlying thestripe are heated by the current flowing through the stripe until theglass obtains a temperature at which the stripe burns off. At thisstage, the heated margins will have attained a temperature at which theglass is electrically conductive so that heating current from theelectrodes now flows through the heated margins.

The corresponding margins of the lower sheet are heated by their closeassociation with the upper sheet and as the heating continues themargins of the upper sheet soften and sag into contacting relationshipwith the margins of the lower sheet. Heating is continued until themargins of both sheets are softened and run together to form acontinuous peripheral weld uniting the assembled sheets. Thereafter thesheets are pulled while the air is moved between the sheets in a knownmanner to bloom the edges of the unit.

Various modes of controlling the heating current supplied to the edgesof the glass sheet have been utilized in the prior art. For example, inU.S. Pat. No. 2,398,360 the applied current is either supplied to allfour edges simultaneously or in a step-by-step fashion to one side afteranother by switching the current from one pair of electrodes to anotherpair. In U.S. Pat. Nos. 3,510,285 and 3,796,556 a switching current ispermitted to flow alternately first through one pair of opposed edges ofthe glass sheets and then through the other pair of opposed edges.

In U.S. Pat. No. 3,628,935 the relay operation of U.S. Pat. No.3,510,285 is eliminated and a saturable reactor circuit applies apolyphase voltage first to one pair of opposite edges and then theremaining pair of opposite edges. U.S. Pat. No. 3,726,658 provides anelectrode arrangement whereby the current flows between diagonallyopposed pairs of electrodes, the diagonals being shifted periodically tochange the flow pattern, while heating all four edges of the glass sheetsimultaneously.

U.S. Pat. No. 3,847,584 teaches that welding current is applied to eachof the side edges in turn of a one of the glass sheets in a firstheating cycle. The current applied to each edge is automaticallycontrolled through a series of four or more potentiometers which areselected in a timed sequence to produce a desired pattern of currentflow and thus a predetermined heating pattern in the selected edgewhereby the edges are gradually and uniformly brought up to a desiredtemperature.

The prior art teachings in general can be grouped into two categories,namely (1) those which teach the sequential heating of the margins ormarginal edge portions of a glass sheet and (2) those which teachapplying a voltage to opposed corners of a glass sheet. Although each ofthese techniques are satisfactory for their intended purposes, there arelimitations. For example, in the practice of sequentially heating themarginal edges, the procedure is slow because current is individuallyapplied to each margin edge until the glass attains the fusingtemperature. Further, the last heated edge is hotter than the firstheated edge. The temperature difference between the first heated edgeand the last heated edge depends on welding time and/or glass size. Asthe welding time for each edge increases and/or the length of the edgeincreases, the temperature difference increases. Further, as thetemperature difference increases, the thickness of the weld varies. Thisis because the hotter glass edge is more viscous and easily shapedwhereas the cooler glass edge is less viscous and more difficult toshape. Nonuniformity of edge thickness decreases edge quality.

The limitation in practicing the diagonal welding technique is that theconductive stripe does not conduct current uniformly because the stripeis not applied uniformly. More particularly, the thickness and/or widthof the conductive stripe sometimes varies, and the electricalconductivity of the stripe varies. The variation of electricalconductivity results in higher heating currents passing through one pairof adjacent edges than through the other pair of adjacent edges. Afterthe stripe is burned off, the pair of adjacent glass edges are atdifferent temperatures and have different electrical resistivity. Theresultant weld is nonuniform for similar reasons discussed above.

As can be appreciated, it would be advantageous, therefore, to provide aprocess of and apparatus for welding edges of glass sheet that does nothave the drawbacks of the prior art.

SUMMARY OF THE INVENTION

This invention relates to a method of heating marginal edge portions ofa glass sheet to a fusing temperature which includes the steps ofsequentially applying an electrical potential to marginal edge portionsof the sheet followed by alternately applying an electrical potential toopposed corners of the sheet.

This invention also relates to a method of fusing glass sheets togetherto form a multiple glazed unit wherein the method includes the steps ofapplying a conductive stripe to marginal edge portions of at least onesheet through which a current is passed to heat the marginal edgeportions of the sheet to a fusing temperature. Thereafter, the heatedmarginal edge portions of the sheets are welded together to form amultiple glazed unit. The improvement includes sequentially passingelectrical current through marginal edge portions of the sheet havingthe conductive stripe followed by alternately passing a current throughopposed corners of the sheet. This invention further relates to anapparatus for heating marginal edge portions of a rectangular glasssheet to a fusing temperature. The apparatus is of the type having anelectrode mounted in spaced relation to each corner of the glass sheetand a source of electrical potential. Electrical connecting anddisconnecting facilities, e.g. contactors, are provided to electricallyconnect or disconnect the electrodes to the source. Facilities, e.g.relays, are provided for acting on the contactors sequentiallyconnecting a pair of adjacent electrodes to the source whileelectrically disconnecting the remaining electrodes from the source andfor alternately connecting an opposed pair of electrodes to the sourcewhile electrically disconnecting the remaining two electrodes from thesource.

Further, this invention relates to an improved glass welding apparatusfor forming multiple glazed units of the type having facilities foraligning a pair of glass sheets and an electrical welding circuit withelectrodes in spaced relation to each corner of a one of the glasssheets. The improvement includes first facilities, e.g. contactors, forelectrically connecting a pair of adjacent electrodes to the weldingcircuit and second facilities, e.g. contactors, for electricallyconnecting a pair of opposed electrodes to the welding circuit.Facilities, e.g. relays, act on the first and second electricallyconnecting facilities to activate a one of the electrically connectingfacilities and deactivating the other one of the electrically connectingfacilities. In this manner, the marginal edge portions are sequentiallyheated and thereafter the marginal edges are simultaneously heated.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic illustration of the overall system of thepresent invention;

FIG. 2 is a diagrammatic and partially schematic illustration of thephase shift controller shown in FIG. 1;

FIG. 3 is a partial schematic diagram of the power regulators of FIG. 1;

FIG. 4 is a partially schematic and partially diagrammatic illustrationof the current trip circuit of FIG. 1.

FIG. 5 is a schematic diagram of the automatic phase shift sequencer ofFIG. 2; and

FIGS. 6A, 6B and 6C are partial schematic diagrams of relay networkwhich controls the operation of the system shown in FIG. 1.

DESCRIPTION OF THE INVENTION

This invention relates to welding edges of a pair of glass sheets toform a glass edge multiple glazed unit. In general, a voltage issequentially imposed on marginal edges of a sheet followed byalternately imposing a voltage on opposed corners of the sheet. Theinstant invention may be practiced by modifying prior acr electricalcircuits and is described by modifying the electrical circuit taught inU.S. Pat. No. 3,847,584 which teachings are hereby incorporated byreference.

Referring to FIG. 1, there is illustrated in diagrammatic form a system10 similar to the system illustrated in FIG. 1 of U.S. Pat. No.3,847,584 and modified in a manner to be discussed below for practicingthe instant invention.

In accordance with the instant invention, an upper glass sheet 12 isaligned over a smaller glass sheet (not shown) in a closely spacedrelation thereto. Prior to heating the edges of the sheet 12 for thewelding process, both sheets are raised to an elevated temperature inthe vicinity of the strain point of the glass sheets. Anelectroconductive stripe 14 is coated on the upper surface 15 of thesheet 12 immediately adjacent the edge thereof and arranged to beproximate to four corner electrodes, 16, 17, 18 and 19, when the glassis in position for the welding operation. The conductive stripe 14 whichis readily dissipated when the temperature of the glass sheets reach thepoint where the glass becomes electroconductive, provides an initiallyhighly conductive path around the marginal edge portions of the glasssheet 12. The four electrodes 16, 17, 18 and 19 are disposedsufficiently near the corners 22, 23, 24, and 25, respectively, of theglass sheet 12 to produce a spark or arc across the short gap to enablecurrent to flow between the electrodes through the conductive stripe 14.Preferably each electrode 16-19 is pointed diagonally in toward theadjacent corner 22-25, respectively, and spaced therefrom of about 1/8inch (0.32 centimeter).

Power is applied to the electrodes 16-19 from secondary 28 of aconventional welding transformer 30 by way of normally open relaycontacts C1a, C2a, C3a, C4a, C5a and C6a. Energization of appropriatecorresponding relay coils permits selected pairs of the electrodes 16-19to be energized to heat the edge portions of the sheet. For example, toheat the marginal edge portions 22-23 of the sheet 12, the contacts C4aand C6a are closed; to heat the marginal edge portions 23-24, thecontacts C6a and C1a are closed; to heat the marginal edge portions24-25, the contacts C1a and C3a are closed; and to heat the marginaledge portions 25-22, the contacts C4a and C3a are closed. In the presentinvention, the successive heating of marginal edge portions, 22-23,23-24, 24-25, and 25-22 constitute a side heating cycle with themarginal edge portions 22-23 and 24-25 being the long sides of the sheet12 and marginal edge portions 23- 24 and 25-22 being the short sides orends of the sheet 12.

After predetermined number of side heating cycles, the power is appliedto selected electrodes to pass current through both short and both longsides of the sheet 12. For example, the marginal edge portions 25-22-23and 23-24-25 are simultaneously heated by closing contacts C6a and C2aand the marginal edge portions 22-23-24 and 24-25-22 are heated byclosing contacts C4a and C5a. In the present invention, thesimultaneously heating of marginal edge portions 25-22-23 and 23-24-25constitutes a first half of a diagonal heating cycle and simultaneouslyheating marginal edge portions 22-23-24 and 24-25-22 constitutes thesecond half of the diagonal heating cycle. As will be appreciated, thefirst half may be the second half and the second half may be the firsthalf of a diagonal heating cycle.

In the practice of the invention, it is recommended that the electrode17 between the first and second marginal edge portions heated and theelectrode 19 between the third and fourth marginal edge portions heatedbe energized for more efficient heating of the marginal edges during thefirst half of the first diagonal heating cycle. For example, if the sideheating cycle heats 22-23; 23-24; 24-25; and 25-22, the contacts C2a andC6a are closed to heat marginal edge portions 23-24-25 and 25-22-23during the first half of the first diagonal heating cycle. Using thisarrangement the current passes through the coldest side and the hottestside, e.g., 22-23 and 22-25, respectively, in the above example andthrough the second and third hottest side, e.g., 24-25 and 23-24,respectively, in the above example. In this manner, the difference ofthe average resistance between each current path is minimized.

Power is applied to the system 10 from a standard source 32 of 60 cyclealternating current which applies a voltage of approximately 460 voltsto a circuit breaker 34, to normally open relay contacts C7a and C7b andacross primary windings 36 of Inductrol transformer 38. The upper end ofthe primary winding 36 is connected by way of line 40 to supplyalternating current power to a long side power regulator 42 and a shortside power regulator 44 which provide control of alternating currentpower for the welding electrodes 16-19 during the side heating cycles.The long side power regulator 42 is used alone during the diagonalheating cycles because there are only long sides.

The phase angle of the output of the long side power regulator 42 iscontrolled by a phase shift controller 46, with the regulator outputbeing applied through a reactor 48 to the upper end of a tappedautotransformer 30. Similarly, the phase angle of the output of theshort power regulator 44 is controlled by the phase shift controller 46and is applied by way of secondary winding 52 of the Inductroltransformer 38 to the upper end of the autotransformer 50. The lower endof the autotransformer 50 is connected to the lower end of the secondarywindings 36 of the Inductrol transformer 38 by line 54 to complete thepower circuit.

The secondary winding 52 of the Inductrol transformer 38 is connected inseries with the output of the short side regulator 44 and acts as avoltage bucking winding to reduce the current applied to theautotransformer 50. The second winding 52 insures that the voltagesupplied to the welding electrodes 16-19 for the short sides e.g., 23-24and 22-25 of the glass sheet 12 is reduced by an amount determined bythe ratio of the primary and secondary windings 36 and 52, respectively,to prevent improper heating, e.g., underheating, of the short sidesduring the side heating cycles.

Autotransformer 50 has a plurality of taps 56 which are connected tocorresponding contacts 58 and 60 on first and second tapping switches 62and 64, respectively, having adjustable wiper arms 66 and 68,respectively. Wiper arm 66 is moveable to feed a selected voltage levelthrough a normally open relay contact C8a to the upper end of primarywinding 70 of the welding transformer 30. Similarly the wiper arm 68 ofthe second tapping switch 64 is connected, by way of normally open relaycontact C9a, also to the upper end of the primary windings 70 of thewelding transformer 30. The lower end of the winding 70 is connected byway of the line 72 to the lower end of the autotransformer 50, to thelower end of the winding 36 by way of the line 54 and through normallyopen relay contact C7b to the source 32.

The first and second tap switches 62 and 64, respectively, permitdifferent voltages to be applied to the welding electrodes 16-19 ondifferent heating cycles. Thus, for example, the contact C8a is closedto supply the input voltage to the welding transformer 30 during theside heating cycles while the contact C9a is closed during the diagonalheating cycles. The side heating cycles occur when the glass isrelatively cool, and thus a higher voltage level is normally selectedfor use than would be the case for the diagonal heating cycles, when theincreased temperature of the glass has reduced its resistance.Typically, a voltage of from 199V. to 460V. may be selected by the tapswitch 62 and 64, with the welding transformer 30 stepping this voltageup to the voltages required for proper current flow. Thus, if the wiperarm 66 of the tap switch 62 is set to the far left as viewed in FIG. 1,a voltage of 460V. would be applied to the primary windings 70 of thewelding transformer 30 resulting in 22,000 volts appearing across thesecondary windings 28. Typically, however, tap switch 62 will be set toproduce a voltage of approximately 17,000 volts across the selectedelectrodes during the side heating cycles, while the tap switch 64 willbe set to produce approximately 10,000 volts across the selectedelectrodes during the diagonal heating cycles. These values are for thelong side of the glass sheet during the side heating cycles. Thesecondary winding 52 of the Inductrol transformer 38 will reduce thesevalues by an amount proportional to the reduced length of the short sideof the glass during the side heating cycles.

The phase shift controller 46 controls the power regulators 42 and 44during the side heating cycles and controls the power regulator 42during the diagonal heating cycles so as to produce effective currentsin the glass being welded which will raise the glass temperature inaccordance with a predetermined selected heating curve. The heatingcurve is produced by a plurality of phase angle controllers such aspotentiometers which are sequentially selected in accordance withpredetermined patterns whereby the power is supplied by the regulators42 and 44 in accordance with not only the cycle in which the system isoperating but the marginal edge or step to which the voltage is beingapplied within a given cycle. The selection of the proper controlsequence is accomplished by way of timers to be described and by way ofsuitable counters which may be of the conventional relay type whichdetect and keep track of the cycle and step in which the system 10 isoperating.

Although not limiting to the invention, a current transformer 74 of thetype taught in U.S. Pat. No. 3,847,584 senses the current flow throughthe line 72 and is responsive to the current flowing through the glasssheet 12 during the side heating cycles and the diagonal heating cycles.The current flowing through the glass sheet 12 is indicative of thetemperature and therefore the output of the current transformer 74 maybe used to operate a current tripping network 76 of the type taught inU.S. Pat. No. 3,847,584 to determine when a selected maximum current isflowing through the glass for any given cycle. In general, when thedetected current exceeds the value set for the cycle, the circuit inside counter and cycle counter 78 operates to shift the counter circuitto the next step for the side heating cycle and to opposite diagonalcorners for the diagonal heating cycle. A dwell time delay network 80 isresponsive to the operation of the current trip network 76 to preventthe next adjacent side from being heated during the side heating cycleand opposite diagonal corners during the diagonal heating cycle untilall of the appropriate relays have been set up.

In the following discussion, the first two heating cycles are sideheating cycles followed by 5 diagonal heating cycles. As will beappreciated, the invention is not limited thereto and any number of sideheating and diagonal heating cycles may be used in the practice of theinvention.

The phase shift controller 46 shown in greater detail in FIG. 2 issimilar to the phase shift controller taught in U.S. Pat. No. 3,847,584.Power is applied to the controller 46 by way of the transformer 82connected to the power source 32 as shown in FIG. 1. This power isapplied across a relay R1, the energization of which is controlled by anormally open relay contact R2a which is closed at the start of awelding operation, thereby energizing the relay R1 to permit operationof the power regulators 42 and 44 for the side heating cycles andoperation of the power regulator 42 for the diagonal heating cycles.Power from secondary winding 84 of the transformer 82 is also appliedthrough parallel windings 86 and 88 which constitute the primarywindings of output transformers for the phase shift controller 46 andthrough a resistor 90 to a plurality of selectably energizerable phaseangle controls generally indicated at 92, 93, 94 and 95. Each of thecontrols 92-95 is connected across the transformer 82 by way of suitablerelay contacts to be discussed below whereby a selected one of thecontrols 92-95 may be connected to the output windings 86 and 88.

In particular, the phase angle controls 92-95 are connected in thecircuit with the selected relay contacts of the cycle counter 78 wherebya selected control function is obtained for each heating cycle. Thus,automatic phase shift sequencer 96 is utilized during the side heatingcycles, e.g., cycles 1 and 2 of the glass heating operation and placedin the control circuit by way of normally open contact R3a of the relayR3 and a normally closed relay contact R4a of relay R4. These relays arein the network of the cycle counter 78 with relay R3 being energized atthe start of cycle 1 of the heating cycle to close the relay contact R3aand place the automatic phase sequencer 96 in series with the outputwindings 86 and 88. This allows the automatic phase sequencer 96 toprovide the output from the phase shift controller 46 during the firstand second side heating cycle whereby the automatic phase shiftsequencer 96 controls the regulators 42 and 44 (see FIG. 1). Aspreviously mentioned during the side heating cycle, sides 22-23, 23-24,24-25 and 25-22, are sequentially heated. At the start of the firstdiagonal heating cycle, contact R4a is shifted to its open position andthe automatic phase shift sequencer 96 is removed from the circuit. Atthe same time, the relay R4 closes its normally open contact R4b tooperate on the long side power regulator 42 by placing potentiometer 98of the phase angle control 93 in series with output windings 86 and 88.The setting of the potentiometer 98 of the phase angle control 93controls the long side power regulator 42 to regulate the current flowthrough the diagonal corners during the first diagonal heating cycle tosimultaneously heat marginal edges 25-22-23 and 23-24-25 during thefirst half of the first diagonal heating cycle and to simultaneouslyheat marginal edge 22-23-24 and 24-25-22 during the second half of thefirst diagonal heating cycle.

At the start of the second diagonal welding cycle relay R5 is energizedopening the relay contacts R5a and closing normal open relay contact R5bplacing the potentiometer 100 of the phase angle control 94 in serieswith the output windings 86 and 88. The setting of the potentiometer 100controls the long side power regulator 42 to regulate the heating of theglass sheet for the second and third diagonal welding cycles in asimilar manner discussed for the first diagonal heating cycle. At theend of the third diagonal welding cycle, relay R6 is energized to shiftto open normally closed relay contacts R6a to remove phase angle control94 from the circuit and closing normally open relay contact R6b to placethe phase angle control circuit 95 in the system. For the remainingdiagonal welding cycles of the heating operation, potentiometer 102 ofthe phase angle control circuit 95 controls the long side powerregulator 42 and thus controls current flow through marginal edges ofthe glass sheet in a similar manner discussed for the first diagonalheating cycle. It has been found that the potentiometers 98, 100 and 102may after initial adjustment be left at fixed settig to provide optimumheating and welding of the glass sheets.

The manner in which (1) the automatic phase shift sequence 96 regulatesthe power supplied by regulators 42 and 44 to the welding transformer 30during the side heating cycles and (2) this potentiometers 98, 100 and102 regulate the power supplied by the regulator 42 during the diagonalwelding cycles to the welding transformer may be seen more clearly inFIG. 3 which is a partial schematic diagram of a preferred form of theregulators 42 and 44.

With specific reference to FIG. 3, the output windings 86 and 88 of thephase shift controller 46 (FIG. 2) is comprised of primary windings ofoutput transformers having secondary windings 104 and 106, respectively,which provide the input to the power regulators 42 and 44 during theside welding cycles and to the long side power regulator 42 during thediagonal heating cycles. One winding provides the input for the positivegoing portion of the alternating current waveform and the other windingprovides the input for the negative going portion of the waveformwhereby a full wave output is obtained from the regulators duringselected welding cycles. The power regulating elements in the long sideregulator 42 which are used during the side welding cycles to heat thelong side of the glass sheet 12 and during the diagonal welding cycleare, in the present embodiment, a pair of ignitrons or gas breakdowntubes 108 and 110. The ignitrons are cross-connected in a parallelopposing circuit to be alternately conductive and produce a full wave ofcontrolled output. In a similar manner, the short side power regulator44 which is used during the side heating cycle to heat the ends of theglass sheet 12 includes a pair of ignitrons 112 and 114 similarlycross-connected for alternate conduction. The selection of the long sideand short side ignitron is by way of relay contacts R7a through R7fresponsive to a normally de-energized relay R7 which is operated toshift all of its contacts when the short side is to be welded during theside welding cycles and is removed by relay contact R26i (FIG. 6A)during the diagonal welding cycles.

Conduction of the ignitrons is controlled by a pair of thyratron gastubes 116 and 118 which are, in turn, controlled by the current level inthe secondary windings 104 and 106, respectively, by way ofcorresponding thyratron control networks 120 and 122. The thyratroncontrol networks 120 and 122 include suitable rectifiers to preventdamage to the igniter electrodes of the ignitrons and prevent damagingreverse currents during the half cycles in which the correspondingignitrons are off. The thyratron control network 120 provides a controlvoltage, the magnitude of which is determined by the input on thetransformer secondary winding 104, to charge a timing capacitor 124which controls the time at which the thyratron fires, and thus controlsthe phase angle of firing. When the thyratron 116 becomes conductive, itapplies a firing voltage to either the igniter electrode 126 of theignitron 108 or the igniter electrode 128 of the ignitron 112, dependingupon the energization of relay R7 thereby firing a correspondingignitron.

In a similar manner, the current from transformer secondary 106 isapplied through thyratron control network 122 to a timing capacitor 130,the time constant of which regulates the firing of thyratron 118. Whenthe tyratron 118 fires, it applies a firing voltage to the igniterelectrode 132 of igniter 110 or to the igniter eletrode 134 of theignitron 114, again depending upon the energization of the relay R7.Thus the magnitude of the current applied to the transformer windings104 and 106 determines the time in each alternating current cycle atwhich the thyratrons 116 and 118 will fire and accordingly, determinesthe phase angle at which the corresponding ignitrons supply power to theautotransformer 50.

It will be seen that to operate the ignitron circuit of FIG. 3, it isfirst necessary to energize relay R1 (FIG. 2) which closes the normallyopen contacts R1a and R1b in series with the thyratrons 116 and 118,respectively. The thyratron 116 is connected through relay contact R1a,normally closed contact R7a and a circuit breaker 136 to the anode ofthe ignitron 108. The cathode of the thyratron 116 is connected to theigniter electrode 126 by way of normally closed contact R7c and to theigniter electrode 128 through normally open contact R7d. The anode ofthe thyratron 118 is connected through relay contact R1b and circuitbreaker 136 to the anode of the ignitron 110 while the cathode of thethyratron is connected by way of normally closed contact R7e to theigniter electrode 132 and through normally open contact R7b to theigniter electrode 134. The anodes and cathodes of ignitrons 108 and 110are cross-connected by way of lines 140 and 142 while the anodes ofignitrons 112 and 114 are cross-connected by lines 144 and 146.

One side of the alternating current source 32 is connected through thecircuit breaker 34, normally open main contact C7a and a line 148 to thecathode of ignitron 112. This side of the source 32 is further connectedthrough the line 144 and connecting line 150 to the cathode of ignitron108. The other side of source 32 is connected through the circuitbreaker 34 and normally open main contact C7b to the line 54 throughwhich alternating current power is applied by way of the transformer 50and secondary winding 52 to the cathode of the ignitron 114 and by wayof transformer 50 and reactor 48 to the cathode of the ignitron 110.

The effective change in the firing angle of an ignitron is fullydiscussed in U.S. Pat. No. 3,847,584 at column 9, line 38, to column 10,line 6, and reference thereto may be made.

As indicated in the discussion of FIG. 1, the current trip network 76senses the current flow to the welding transformer 30 and when apredetermined level of current flow is reached for each step of the sidewelding cycle and diagonal welding cycle produces a stepping signalwhich shifts the welding operation to the next adjacent side of theglass for the side welding cycle and to the opposite set of diagonalcorners for the diagonal welding cycle. In order to establish a desiredcurrent maximum for each cycle, a plurality of reference voltages areset up by the current trip network 76 and selected by relays of thecycle counter 78 to keep track of the cycles of the welding operation.

The current trip network taught in U.S. Pat. No. 3,847,584 in column 10,line 7, to column 11, line 14, and in U.S. Pat. Application Ser. No.836,258 filed even date in the name of M. E. Klockenga for "Method ofand Apparatus For Selectively Heating An Edge of a Glass Sheet During aWelding Program" may be used in the practice of the invention. Thecurrent trip network 76 shown in FIG. 4 is of the type taught in theabove-mentioned U.S. patent application filed in the name of M.Klockenga.

With reference to FIG. 4, the output for the current sensing transformer74 is applied by way of lines 152 and 154 across an input resistor 156to the current trip network 76. Line 152 is connected by way of line 158to a suitable rectifier and filter network 160 to provide a referencevoltage on line 162. A plurality of potentiometers 164-171 used in thepreferred embodiment of the present welding system are connected inparallel between lines 162 and 152. The potentiometer 164 is used duringthe first side welding; the potentiometers 165 and 166 are used duringthe second or last side welding cycle. As can be appreciated theinvention is not limited to the number of side welding cycles,therefore, should more than two side welding cycles be employed,potentiometers for each additional side welding cycle similar to thepotentiometer 164 would be used. The potentiometer 167 is used duringthe first diagonal welding cycle and the potentiometers 168-171 areemployed during the remaining four diagonal welding cycles. Further ascan be appreciated, the invention is not limited to the number ofdiagonal welding cycles and although the current trip network 76 shownin FIG. 4 is arranged for five diagonal welding cycles, the invention isnot limited thereto and may be used with more or less than five diagonalwelding cycles.

The line 154 is connected through a normally closed contact R8a toprimary winding 174 of a transformer 176, the opposite side of which isconnected to the line 152. Secondary winding 178 of the transformer 176is connected between the line 152 and anode 180 of a gas diode 182.Cathode 184 of the gas diode 182 is connected to the line 152. The anode180 of the gas diode 182 is connected by way of line 186 to a resistor188 to a common output line 190 from the adjustable arms of thepotentiometers 164-171.

The adjustable arm of each potentiometer 164-171 is connected through tosuitable contacts of relays R4, R5, R6, R9, R10, R11, R12 and R13 in thecycle counter 78 (FIG. 1). During the first side welding cycle relaycontact R9a is closed and contacts R9b, R10b, R11b, R5d, R12d, R6d,R13b, and R4d and are open to remove potentiometers 165-171 from thecircuit. During the second side heating cycle; i.e., the last sidewelding cycle, contact relay R9 is energized to open relay contact R9aand close contact R9b to remove the potentiometer 164 from the circuitand connect the potentiometer 165 to the circuit through normally closedrelay contacts R4c and R10a. Potentiometer 165 is in the circuit forheating of sides 22-23, and 23-24 during the first two steps of thesecond side welding cycle. For the heating of the third side; i.e., size24-25 during the last or second side welding cycle, relay contact R10ais open and normally open relay contact R10 b is closed. Potentiometer166 is now in the circuit by way of closed relay contact R10b, normallyclosed contact R11a closed contact R9b, and normally closed contact R4c.Potentiometer 165 is removed from the circuit by open relay contact R10aand R11b. After the side 24-25 is heated, the relay R11 is energized toopen relay contact R11a and close normally open contact R11b. Thepotentiometer 166 is removed from the circuit and the potentiometer 165is back in the circuit by way of closed contacts R4c, R9b and R11b forheating side 25-22 of the sheet 12.

As taught in the above-mentioned U.S. Patent Application, during thelast side welding cycle, the heating of each marginal edge is performedto optimize the subsequent diagonal heating cycle. During the last sidewelding cycle, sides 22-23, 23-24, 24-25 and 25-22 are successivelyheated. As side 23-24 is heated, side 22-23 cools and as side 24-25 isheated, sides 22-23 and 23-24 cool, etc. If the subsequent heating cycleinvolved individual marginal edges, the above procedure would beacceptable; however, when going from a side welding cycle to a diagonalwelding cycle, the average resistance of the two current paths fordiagonal welding should be approximately equal for optimum heating.Therefore, it is preferred that the long side 24-25 be heated for ashorter time than long side 22-23 so that its temperature and thereforeresistance nearly approximates the temperature of the side 22-23previously heated. In other words, the resistance of sides 25-22-23 isapproximately equal to the resistance in sides 23-24-25.

After the second side welding cycle is completed, the relay R4 isenergized to open relay contact R4c and close normally open relaycontact R4d to put the potentiometer 167 in the circuit by way ofnormally closed relay contact R5c. After the first diagonal weldingcycle is completed, the relay R5 is energized to open relay contact R5cand close normally open relay contact R5d. The potentiometer 168 is nowin the circuit by way of normally closed contact R12a and closed relaycontact R5d. After the second diagonal welding cycle is completed,normally closed relay R12a is open and normally open relay R12b isclosed to remove the potentiometer 168 from the circuit and put thepotentiometer 169 in the circuit by way of normally closed relay R6c andclosed relay contact R12b. After the third diagonal welding cycle,normally closed relay R6c is open and normally open relay contact R6d isclosed. The potentiometer 169 is removed from the circuit and thepotentiometer 170 is put in the circuit by way of closed relay contactR6d and normally closed relay R13a. After the fourth welding cycle, thenormally closed relay R13a is open and the normally open relay R13b isclosed to remove the potentiometer 170 from the circuit and put thepotentiometer 171 in the circuit for the fifth diagonal welding cycle.

The potentiometers 164-171 are each adjusted for the desired currentlevel in their corresponding cycles and during the welding operation aresequenced to provide the required control. Whenever the current leveldetected by the transformer 74 exceeds the level preset by thecorresponding cycle potentiometer, a voltage detector network 192 isenergized to shift the operation to the next marginal edge of the glassas has been explained. More particularly, to the next marginal edgeduring the first side welding cycle, between the potentiometers 165 and166 during the last side welding cycle and to opposite diagonal cornersduring the diagonal welding cycles.

It was noted with respect to the phase shift controller 46 illustratedin FIG. 2 that although the diagonal welding cycle of the normal weldingoperation utilized fixed current values (and thus fixed firing anglesfor the long side power regulator 42) as determined by the settings ofthe potentiometers 98, 100 and 102, the side welding cycles, i.e., thefirst two cycles, require different approach since the relatively coolglass has during the initial period of heating a relatively highresistance to current flow. Accordingly, in place of a fixedpotentiometer the automatic phase shift sequence 96 is preferred duringthe first two cycles, i.e., the side welding cycles for regulating thefiring angle of the power regulators 42 and 44. It has been known in thepast to utilize for cycles 1 and 2 a manually adjustable potentiometerpositioned at the glass welding location for adjustment by an operatorwho observes the progress of the welding during the side welding cyclesand adjusts the potentiometer accordingly to produce the desired weldingresults. As can be appreciated, however, such manual operation presentsserious difficulties for not only does it require very skilled operatorsto obtain optimum results but in addition it is difficult even with theskilled operator to obtain uniform results each time. Variations in thequality of the glass unit produced by a manual system become morepronounced and when one operator replaces another as in the change ofshifts where less skilled operator may replace a more skilled operator.It is, therefore, recommended that the automatic phase shift sequencertaught in U.S. Pat. No. 3,847,584 be used in the practice of theinvention.

With reference to FIG. 5, the automatic phase sequencer 96 of the typetaught in U.S. Pat. No. 3,847,584 includes a plurality of adjustablepotentiometers 222-226 which are connected to suitable sequence relaycontacts between line 228 and a common line 230. Potentiometer 222 isconnected between the lines 228 and 230 by way of normally open relaycontact R14a and normally closed contact R15a, with the movable arm ofthe potentiometer 222 being adjustable to place a selected resistance inthe line. When both relay contact R14a and R15a are closed, theresistance value of the potentiometer 222 is placed in series with theline 228 and when the automatic phase sequencer 96 is selected by thesimultaneous closure of relay contacts R2a and R3a (FIG. 2) theresistance value of the potentiometer 222 determines the firing angle ofthe power regulators 42 and 44 (FIGS. 1 and 3) and thus determines thecurrent level applied to marginal edge portion of the glass beingwelded. In similar manner, potentiometer 223 is connected across lines228 and 230 by way of normally closed relay contact R16a, normally openrelay contact R15b; potentiometer 224 is connected by way of normallyopen relay contact R16b and normally closed relay contact R17a; and thepotentiometer 225 is connected by way of normally open relay contact R17b and normally closed relay contact R18a. The manually adjustableoperator potentiometer 226 overrides or supplements the automatic phaseshift sequencer. The potentiometer 226 is connected across the lines 228and 226 by way of either a normally open relay contact R18b or normallyclosed relay contact R14b, these contacts being connected in parallelwith each other.

It will be seen that when none of the relays R14, R15, R16, R17 and R18are energized, none of the potentiometers 222-225 will be connected tothe line 228 whereas the operator potentiometer 226 will be connectedthrough normally closed relay contact R14b to the line 230.

For a complete discussion of the operation of the automatic phasesequence, reference may be made to column 11, line 15, to column 12,line 21 of U.S. Pat. No. 3,847,584.

It has been found that during the diagonal welding cycles, a side of theglass sheet may be lower in temperature than the remaining sides. Whenthis occurs, the cooler side does not fuse properly. The discussion willnow by directed to a circuit to interrupt the diagonal welding cycle toheat a single side that may be used in the practice of the invention.

The circuit of the above-mentioned patent application is schematicallyshown in FIG. 6B discussed below. In general, the circuit shown in FIG.6B is used during the diagonal welding cycles to interrupt the diagonalweld after the completion of a half cycle to heat a selected side. Thismay be accomplished by moving a toggle switch stick 232 to one of fourpositions each corresponding to a side of the sheet to close itsrespective contacts 234-237. For example, for heating side 22-23,contacts 234 of the switch 232 are closed; for heating side 23-24,contacts 235 of the switch 232 are closed; for heating side 24-25,contacts 236 of the switch 232 are closed and for heating side 25-22,contacts 237 of the switch 232 are closed. Through a series of relaysand relay contacts, the current trip 76 is removed from the circuit anda selected side is heated. When the side is heated to the desiredtemperature, as indicated by visual inspection of the side, the switch232 is released to continue the diagonal welding cycle.

Shown in FIGS. 6A and 6B are the relay controls for the overall circuitoperation, while FIG. 6C in general includes the sequencing relays forthe automatic phase shift sequencer 96. As shown in FIG. 6A, thealternting current is applied from power source 32 through powertransformer 240 across lines 224 and 242, between which the controlrelays are connected. It will be understood that although the relaynetwork illustrated in FIGS. 6A-6C includes the major features of thepresent system, a number of auxiliary features such as safety relays,temperature controllers for the ignitrons, cooling water thermostats,test relays, indicator lights, and the like have been eliminated inorder to simplify the system and make it more readily understandable.

Start and stop switches 246 and 248, respectively, are provided for thewelding system to energize relays R2 and R19, respectively, byconnecting them across lines 242 and 244. Stop relay R19 includes aninterlocked relay contact R19a in series with the relay R2 to insurethat relays R2 and R19 cannot be energized at the same time. When therelay R2 is energized by depressing the push button 246 its normallyopen relay contact R2b is shifted to the closed position to energize themain contactor C7 to close its normally open contacts C7a and C7b(FIG. 1) to applying alternating current to the welding system 10 ofFIG. 1. One or the other of the high and low range selector controls C8and C9 is then energized by the network 250, thereby placing either thefirst or second tap switches 62 and 64 in series with the weldingtransformer 30. The energization of the contactors C8 and C9 isdetermined by the cycle counting section 252 (FIG. 6A) of the sidecounter and cycle counter 78 (FIG. 1) which incorporates the relaysR3-R6, R9-R13, and R20-R23 connected in known manner to keep track ofand to control the cycle in which the welding system is operating. Thecontactor C8 is operated during the first two cycles, i.e., side weldingcycles and the contactor C9 during the remainder cycles, i.e., diagonalwelding cycles in the embodiment described herein.

The discussion will now be directed to the operation of contactors C1through C6 during the side welding cycles and diagonal welding cycles.During the welding cycle, welding contacts C1 through C6 are energizedby normally closed relay contacts R26a, R24a, R27b, R26c, R25a, R26d andR27d and normally open relay contacts R27a, R24b, R25b, R26b, R26e, andR27c, responsive to relays R26, R24, R27 and R25 in the side counterportion 254 of the side counter and cycle counter 78. At the start ofthe side weld cycle, contactor C4 is energized by normally closed relaycontacts R26a and R24a and contactor C6 is energized by normally closedrelay contacts R26c and R25a. Energization of contactors C4 and C6 closecontacts C4a and C6a, respectively, to apply voltage to the electrodes16 and 17 to heat the long side 22-23 of the sheet 12. After the side22-23 is heated to the desired temperature as indicated by the currenttransformer 74, the side counter 254 operates to energize the relay R24to open the relay contact R24a to de-energize the contactor C4 and closenormally open relay contact R24b to energize the contactor C1. Thecontact C1a closes and a voltage is applied to electrodes 17-18 to heatthe short side 23-24 of the sheet. After the side 23-24 is heated to thedesired temperature, the relay R25 is energized to open the closed relaycontact R25a to de-energize the contactor C6 and close normally openrelay contact R25b to energize contactor C3 to close normally opencontact C3a. Voltage is applied to the long side 24-25 by way ofelectrodes 18 and 19. After the side 24-25 is heated to the desiredtemperature, the relay R24 is de-energized to open relay contact R24b tode-energize contactor C1 and to close contact R24a to energize contactorC4 to close contactor C4a to apply a voltage to electrodes 16 and 19 toheat the short side 22-25 of the sheet to complete one side weldingcycle. During the first side welding cycle, the conductive stripe isburned off and the temperature of the glass increased to reduce itselectrical resistance.

If during the automatic side welding cycle the operator determines thatfor some reason a weld is not complete, a side hold push button 256 isprovided which permits an override of the stepping operation bydisabling the current tripping network 76. Thus, by depressing switch256, the operator energizes relay R8 to open relay contact R8a (FIG. 4)thereby preventing the current trip network from detecting the currentlevel in the welding transformer. When this is the case, the currentflow through the marginal edge portion being welded is continued untilthe operator releases the push button 256 and contact R8a recloses toplace the current trip network in the circuit.

The relays in the side counter 254 operate in a similar manner duringthe side welding cycle. However, on the last side weld cycle, the cyclecounter relays operate on the current trip network 76 (FIG. 4) toenergize the relay R9 to open normally closed relay contact R9a andclose normally open relay contact R9b to put the output of potentiometer165 into line 190 during the heating of sides 22-23 and 23-24. After theheating of side 23-24, the cycle counter 252 energizes the relay R10 toopen normally closed relay contact R10a to remove the potentiometer 165from the circuit and to close normally open relay contact R10b to putpotentiometer 166 in the circuit. The potentiometer 166 is set forheating the side 24-25 to a lower temperature during the last sidewelding cycle for the reasons discussed above. After the sides 24-25 isheated, the cycle counter energizes relay R11 to open normally closedrelay contact R11a to remove the potentiometer 166 and to close normallyopen relay contact R11b to put potentiometer 165 back in the circuit forthe heating of short side 25-22.

As taught in U.S. Pat. No. 3,847,584, during the welding side cycle, ithas been found to be unnecessary to heat each side on every side weldingcycle of the welding operation. Accordingly, relay R43 is provided whichwhen energized causes the side counter 254 to operate in such a mannerthat no current is passed through sides 23-24 or 25-22. As illustrated,toggle switches 258 and 260 may be provided to cause relay R43 to beenergized during the first or second side heating cycle. The relaycontacts R3b, R4a, R9a and R9b are provided to enable one or both thetoggle switches 258 and 260 to operate relay R43 during the first orsecond side heating cycles.

The discussion will now be directed to the operation of the contactorsC1 through C6 during the diagonal welding cycles. At the end of the lastside welding cycle, relay contacts R24a, R25b, R26a, R26c, R27b, R26d,and R27d are closed to energize contactors C3 and C4, and the relaycontacts R24b, R25a, R26b, R27a and R27c are open to de-energizecontactors C1, C2, C5 and C6.

After the heating of the side 25-22 for the last side heating cycle,relay R26 is energized to open normally closed relay contacts R26a, R26cand R26d to de-energize contactors C4 and C3 respectively and to closenormally open relay contacts R26b and R26e to energize contactor C6 andC2 to close contacts C6a and C2a, respectively. Contact R26i also opensto keep relay R7 de-energized to insure that only long side voltage willbe applied. Voltage is applied through contacts C6a and C2a toelectrodes 17 and 19 to heat side 23-24-25 and 25-22-23, for the firsthalf of the diagonal welding cycle. At the end of the first half of thediagonal welding cycle, the relay R27 is energized to open normallyclosed relays R27b and R27d to de-energize contactors C6 and C2 and toclose normally open relay contacts R27a and R27c to energize contactorC5 and C4 to contacts C5a and C4a respectively, to heat the sides24-25-22 and 24-23-22 to complete the second half of the diagonalwelding cycle.

If during the automatic operation of the diagonal welding cycle theoperator visually determines that the four marginal edges beingsimultaneously welded are not properly fusing together, he can push theside hold button 256 which permits an override of the stepping networkby disabling current trip network 76. Depressing switch 256 energizesthe relay R8 to open the relay R8a contact thereby preventing thecurrent trip network 76 from detecting the current level in the weldingtransformer. When this occurs, the current continues to flow through allfour marginal edges until the operator releases the push button 256 andcontact R8a recloses to place the current trip network 76 back in thecircuit. In this manner, the operator can increase the temperature ofall four marginal edges.

On the other hand, if the operator visually determines during theautomatic operation of the diagonal welding cycle that a weld is notacceptable in one of the four marginal edges, the circuit shown in FIG.6B is employed.

In the way of illustrating the operation of the circuit of FIG. 6B it isassumed that the welder is on the first half of the fourth weldingcycle, i.e., the second diagonal welding cycle, and, therefore, theoff/on switch 262 and relay contacts R4c, R28a and R28b are closed toheat sides 23-22-25 and 23-24-25. From visual inspection, it isdetermined that side 22-23 of sheet 12 is not fusing properly to thelower sheet because side 22-23 is not sufficiently hot. The toggleswitch 232 is moved to close contacts 234. Current flows from line 242through the closed relay contact R4c, the closed switch 262, the closedrelay contact R28b, and through the closed contacts 234 of the toggleswitch 232 to energize relay R29 connected at one side to the line 244.

Energization of the relay R29 shifts closes its normally open relaycontacts R29b, R29c, R29d and R29e and opens its normally closed relaycontact R29a. The relay contact R26j is open when R26 is energized forthe diagonal welding cycles. The first half cycle of diagonal weldingcontinues until the current trip 76 senses that the proper current hasbeen reached and turns off the welder to switch to the second half cycleof diagonal welding. When this occurs, the relay R28 de-energizes andits contact R28a shifts to de-energize the relay R26 because contactsR28a and R29a are now open.

The relay R29 remains energized through the relay contact R4c, theswitch 262, relay contact R29b and the contact 234 of the switch 232.When the relay R26 de-energizes its relay contact R26j closes and therelay R30 is energized through now closed relay contacts R26j and R29e.At the same time, the relay R8 is energized through relay contacts R29dand R26f (FIG. 6A). The contacts of the relay R30 shift and clear therelays in the side counter 254.

When R26 is de-energized, it opens its closed relay contact R26e andcloses its open relay contacts R26a, R26c and R26d. The contactor C2 isde-energized, the contactor C4 is energized and the contactor C6 remainsenergized.

The above occurs before dwell-timer TDI times out. When TDI times out,its contacts close to energize relay R31 to start the weld again. Longside welding voltage is applied to the electrodes 16 and 17 throughcontactors C6a and C4a to flow current through marginal edge portions22-23. Current continues to flow because the current trip 76 has beendisabled by energized relay R8 which opened its normally closed relaycontact R8a (FIG. 4) to prevent current trip. When the operatordetermines that sufficient temperature has been added to side 22-23, thetoggle switch 232 is released to open its contacts 234. The relay R29 isde-energized to de-energized relay R8 which reactivates the current trip76 by closing the relay contacts R8a. When sufficient current flows toactivate the current trip, relay R28 is de-energized becase the welderis no longer firing. When this occurs, the relay R30 is de-energized byopening closed relay contact R28d. At the same time, the relay R26energizes because relay contacts R28e, R29a, R32a, R34a, R36a close. Therelay R30 de-energizing activates the side counter 254 putting it backon diagonal corners 23 and 25. When the relay R26 energizes, itscontacts shift de-energizing the contactor C4 to open contact C4a andenergizing the contactor C2 to close contact C2a because relays R24, R25and R27 are de-energized by the side counter circuit 254. Dwell-timerTDI times out and contact TD1a closes energizing R31 to start the weld.Voltage is applied to diagonal corners 25 and 23 and current begins toflow in all four edges. The welder is back to normal automatic diagonalwelding.

Assume now that the side 24-25 requires additional heat. The switch 232is moved to close its contacts 236 to energize relay R32. The relays R32and R33 then work together at the proper time to de-energize the relayR26 and energize the relay R8. The relay R33 clears the side counter 254and also energizes the side counter relays R24 and R25 to close relaycontacts R24b and R25b to energize contactors C1 and C3 to closecontacts C1a and C3a, respectively. The welder passes voltage throughelectrodes 18 and 19 to heat the side 24-25 of the sheet. When the longside 24-25 of the sheet is heated to the desired temperature, the switch232 is released to open the contact 236. The trip circuit 76 isreactivated by closing the relay contact R8a; and when sufficientcurrent is reached, as determined by the current transformer 74, thewelder turns off. The relay R33 is de-energized by opening relay contactR28d when the relay R28 is de-energized by the welder turning off. Therelay contact R28e also closes energizing relay R26, and the welder isback on the first half of the diagonal welding cycle.

Assuming now that during the first half of the diagonal welding cycle,the operator determines that short side 23-24 is below the desiredtemperature. The switch 232 is operated to close the contacts 235 toenergize the relay R34. The relay contacts R34a opens and relay contactsR34b-R34e close. The first half of the diagonal welding cycle continuesuntil the current trip 76 indicates the sides are heated to the desiredtemperature and turns the welder off to switch to the second half of thediagonal welding cycle. When this occurs, the relay R28 de-energizes toshift its contact R28a to de-energize the relay R26 because contact R34ais open. The relay R34 remains energized through the relay contact R4c,the switch 262, relay contact R34b and the contact 235 of the switch232. When the relay R26 de-energizes its relay contact, R26j closes andthe relay R35 is energized through now closed relay contact R34e. Therelay R35 is energized and switches its contacts R35a and R35b. Closingthe relay contact R35b energizes the relay R7 to switch its contacts andput the short side power regulator 44 in the system. The contacts of therelay R35 also clear the relays in the side counter 254.

When the relay R26 is de-energized, it opens its closed relay contactsR26e and closes its open relay contacts R26a, R26c and R26d. Thecontactor C2 is de-energized and contactor C6 remains energized whilethe contactor C1 is energized by the energization of relay R24. Thecontactor C1 closes contact C1a and voltage is applied to the side 23-24through electrodes 17 and 18.

When the side 23-24 is at the desired temperature, the switch 232 isreleased to open its contacts 236 to de-energize the relay R32 whichde-energizes relay R8. When current trip occurs, R28e closes to energizerelay R26 because contact R32a is already closed. The welder is now backto diagonal welding.

The relays R36 and R37 for heating the short side 25-22 operate in asimilar manner as the relays R34 and R35 for heating the short side24-23 except that contactor C4 and C3 are energized to close contactsC4a and C3a. In this manner, voltage is applied through electrodes 16and 19 to heat the short side 22-25.

The voltage detector 192, which forms a part of the current trip network76, incorporates a flip-flop circuit (not shown) which is responsive toa current tripping signal to shift momentarily from a steady statecondition to an unstable condition at which time it produces a signalwhich operates the relays of the side counter 254 to shift the weldingcurrent from one marginal portion of the glass to the next during theside heating welding cycles and to shift from one pair of diagonalcorners to the next for the diagonal heating cycles. During the steadystate of the voltage detector flip-flop, a relay R38 is energized. Itscontacts R38a close and the relay R28 is energized. When a current tripcondition occurs, R38 is de-energized and R38a is open momentarily tode-energize the relay R28. The relay contacts R38b in series with thedwell-time delay TDI are momentarily closed and with relay R2 energizedduring normal operation and contacts R2b consequently closed. TDI isenergized to initiate dwell-timing sequence to insure delay between thecurrent trip condition and the start of the next cycle. At the end ofthe preset delay, relay TDI times out and its corresponding contact TD1acloses to energize relay R31 which is the weld starting relay.Energization of the relay R31 allows the flip-flop in the voltagedetector to return to its stable condition, whereby R38 returns to itsenergized condition, thereby energizing the relay R28 and initiateheating of the adjacent side for the side welding cycles and shifting todiagonal corners for the diagonal welding cycles.

The relay R7 which controls the firing of the short side ignitron powerregulator during the side heating cycles by shifting relay contacts R7athrough R7f (FIG. 3) is connected in series with the normally closedrelay R43a contact, the normally open contact R39a, and the normallyclosed relay contact R26i. The relay contact R43a is open only duringthe side heating cycles when the relay R43 is energized to indicate thatthe ends of the glass are to be skipped during the side welding cycle inwhich case the short side power regulator is not required. When the endsare to be heated at the normal heating cycle, side counter relay R39will be energized at the appropriate time to close contacts R38a andshift the relay contacts of the relay R7 so that the power regulator 44is placed in circuit with the autotransformer 50 in place of the longside power regulator 42 during the side welding cycles. When thediagonal welding cycles begin, R26 is energized shifting contact R26i toits open position. This disables the short side firing network so thatonly long side voltage can be applied. The sequencing relays for theautomatic phase sequencer 96 (FIG. 5) are diagrammed in FIG. 7C wherethe main switch SS1 is provided in the power line 242 to permit theautomatic sequencer to be removed from the circuit if desired. When theswitch SS1 is open, the relay network of FIG. 7C is removed from thephase shift control system and phase control of the power regulatorreverts to a manual control by the operator potentiometer 226 (FIG. 5)through the normally closed contacts R14b. The relay R14 is shown inFIG. 6C as being connected across power lines 242-244 by way of normallyclosed switch SS2 or the normally closed relay contact R9c which isconnected in parallel with switch SS2.

It will be recalled that relays R3-R6, R9, R12, R13 and R20-R23 are thecycle counter relays 252 which are energized during the correspondingcycles. Thus, during the first side heating cycle, the relay R9 is notenergized and, therefore, contact R9c remains closed; however, on thesecond cycle of operation, the relay R9 is energized to open the relaycontact R9c and thereby open one of the energization paths to relay R14.The switch SS2 is a cycle skip switch and when open causes the relay R14to be de-energized on the second side heating cycle, thus placingcontrol of the heating current cycle 2 on the operator potentiometer 226(FIG. 6). Since in the present embodiment, the automatic phase shiftsequencer is to be operative only during the first two side heatingcycles, the relay contact R4e is connected in series between theparallel arrangement of switch SS2 and contactor, the relay contact R9cand the remainder of the relay network, so that at the start of thethird cycle or first diagonal welding cycle and the consequentenergization of the relay R4, the relay network is disabled.

During the side heating cycles with either/or both of switches SS2 andthe relay contact R9c closed, power is applied through normally closedrelay contact R4e to power line 264 to energize selective ones of relaysR40, R41 and R42. These relays are energized when heating currents areapplied to the short sides of the glass sheet during cycle 1, the longsides during cycle 2 or the short sides during cycle 2, respectively, tomodify the operation of the remainder of the relay network as will bedescribed. The cycle 1 short side relay R40 is connected between lines264 and 244 by normally closed relay contact R9d and normally open relaycontact R7g. Since the relay contact R7g is a short side relay and isenergized only when the short side of the glass is to be heated andsince the relay R9 is energized during the second cycle, it will beapparent that the relay R40 can be energized during cycle 1 only andonly when the short sides of the glass are being heated. Similarly, thecycle 2 long side relay R41 is connected to the line 264 by way ofnormally closed relay contact R7h and normally open cycle relay contactR9e, and the cycle 2. Short side relay R40 is connected to the line 264through normally open relay contact R7i and normally open relay contactR9e. Accordingly, the relays R41 and R42 can be energized only duringthe second cycle with the particular relay energized being dependentupon whether the short side relay R7 is energized.

The actual firing of the power regulators 42 and 44 is controlled by therelay R28 which is energized only when the voltage detector relay R38(FIG. 4) is energized to indicate that the system is ready for thewelding operation. The relay R28 is thus de-energized and re-energizedbetween each heating step, with the dwell-time delay timer TDIregulating through the relays R31 and R38, the off time betweensuccessive applications of power, or duty cycles, of the powerregulator. Energization of the relay R28, therefore, indicates thewelding system is ready for the next sequencing operation of theautomatic phase sequence 96. Accordingly, the relay contact R28a isclosed to connect power from the line 264 to line 266.

At the start of the heating operation with main switches SS1 closed andfiring relay R28 energized, power is applied to the relay R14 to closeits contacts R14a (FIG. 5) and to place potentiometer 222 across lines228 and 230 of the phase shift controller 46 (FIG. 2) whereby thesetting of the potentiometer 222 regulates the firing angle of the powerregulator 42 to control the effective current along the side 22-23 ofthe glass sheet. At the same time, timer TD2 (FIG. 7C) is energized tocontrol the length of time the potentiometer 222 remains in the circuit.When timer TD2 times out, its contact TD2a closes to connect timer TD3across the lines 266 and 244 for energization and further energizes therelay R15. This opens the relay contact R15a (FIG. 5) and closescontacts R15b thereby replacing the potentiometer 222 with thepotentiometer 223 to thereby adjust the firing angle of the powerregulator 42 in accordance with the setting of the potentiometer 223.This potentiometer remains in the control circuit until timer TD3 timesout, causing contact TD3a to close and energize timer TD4 and the relayR16 opening contact R16a (FIG. 5) to remove potentiometer 223 from thecontrol circuit and closing the relay contact R16b to connectpotentiometer 224 across the lines 228 and 230. The relay R16 alsocloses its contact R16c to maintain the energization of the relay R15 tohold potentiometer 222 out of the control circuit.

When the timer TD4 times out, its contact TD4a is closed to energize therelay R17 and start timer TD5. The energization of the relay R17 opensits contacts R17a to remove the potentiometer 224 from the circuit,closes its contact R17b so that the potentiometer 225 is placed incontrol of the firing angle of the power regulator 42 and closes contactR17c to hold the relay R16 in its energized state and prevent thepotentiometers 222 and 223 from affecting the power regulator 42. WhenTD5 times out, it closes its contact TD5a to energize the relay R18which shifts its contacts to open the relay contact R18a and remove thepotentiometer 225 from the control circuit replacing it with manuallycontrolled operator's potentiometer 226 by way of the relay contactR18b. Again the relay contact R18c holds the relay R17 to prevent thepotentiometers 222, 223 or 224 from affecting the control circuit. Theoperator's potentiometer remains in control of the power regulator 42until the current level through side 22-23 reaches the trip level atwhich time the current trip current 76 produces a signal that thevoltage detector 192 which de-energizes the relay R38 opening its relaycontact R38a and de-energizing R28 thereby removing power from the line266 and resetting the relay system of FIG. 7C. The side counter relaysgenerally indicated in FIG. 7A are then operated to shift the system toside 23-24 of the glass sheet.

Since side 23-24 is a short side, the relay R7 is now energized todisconnect long side power regulator 42 and connect short side powerregulator 44 into the welding system. At the same time, the relaycontact R7g (FIG. 6C) is closed to energize the relay R40. At the end ofthe dwell time set by timer TD1, the relay R28 is re-energized and thesecond step of the first heating cycle commences. Again, the relay R14and time delay TD2 are energized; but since the relay R40 is alsoenergized, the normally open contacts R40a are closed to bypass contactTD2a. Accordingly relay R15 and timer TD3 are immediately energized,without waiting for TD2 to time out, placing potentiometer 223 in thecontrol circuit. The energization of the relay R40 also closes contactR40b which is in series with a selector switch SS3. This switch, whenclosed, energizes the relay R16 and time delay TD4 to bypass the relayR15 and timer delay TD3, thereby permitting the short side to beinitially heated under the control of potentiometer 224. Similarly, aswitch SS4 in series with the relay contact R40c is provided to permitthe short side heating sequence to start on the potentiometer 225 byinitially energizing the relay R17, and timer TD5. Accordingly, on theshort side heating steps of cycle 1, the potentiometer 222 is skipped;and if switches SS3 and SS4 are closed, potentiometers 223 and 224 mayalso be skipped.

On the cycle 1, short side step, the selected timer TD3, TD4, or TD5times out and shifts the control to the next higher potentiometer, andits corresponding timer in the manner described above, with thissequence continuing as before until a current trip signal is produced atthe voltage detector 192 (FIG. 4). When trip occurs, the counter relaysshift to the third step, which is the side 24-25 of the glass, and therelay R28 is de-energized to reset the sequencing relays of FIG. 6C.Short side relay R7 is de-energized; and after time delay timer TD1 hastimed out, the potentiometers 222 and 226 are sequenced as describedwith respect to the side 22-23 to vary the firing angle of the long sidepower regulator 42 in accordance with the settings of thesepotentiometers, producing the desired heating curve in side 24-25. Whencurrent trip occurs, the system is reset and again the side counterrelays energize the R7 relay to repeat the short side sequence for theside 25-22. The current trip which occurs at the end of the fourthheating step, at side 25-22 of the glass, completes the first cycle andthe stepping of the relays of the side counter 254 then operates thecycle counter 252 to energize the relay coil R9 and set the system upfor the second automatic side welding cycle.

Energization of the relay R9 opens contacts R9c and R9d while closingthe relay contact R9e, thereby removing the relay R40 from the controlcircuit and permitting energization of either relay R41 and R42. Sincethe relays of the side counter relays 254 have now stepped back to thefirst side, which is the long side 22-23, the relay R41 is energized.Upon closure of the relay contact R28a, the second heating cycle begins.As before, the relay R14 and timer TD2 are energized; but because of theenergization of cycle relay R9, contact R9b is now closed to energizethe timer TD4 and the relay R16, thus placing the potentiometer 224 inthe control circuit. The energization of R16 removes the potentiometer223 from the circuit, while the relay contact R16c energizes the relayR15 to remove the potentiometer 222 from the control circuit. Thus, thesecond cycle automatically starts under the control of the potentiometer224, producing a higher effective initial current to the glass.

Although the timers TD2 and then TD3 continue to operate in thepreviously discussed way, the energization of the relays R15 and R16prevent them from having any effect on the control circuit. When thetimer TD4 times out, however, the relay R17 and timer TD5 are energizedto sequence the control to the potentiometer 225 and when TD5 times outcontrol is shifted to potentiometer 226 until current trip occurs. Itwill be noted that because the relay R41 is energized during the longside heating step in cycle 2, the relay contact R41b is closed, so thatselector switch SS5 can be closed to directly energize the relay R17 andtimer TD5, whereby the second cycle long side heating can be started onthe potentiometer 226, if desired.

When the tripping current is attained in side 22-23, cycle 2, the systemis stepped to the short side 23-24 to energize the relay R42. Uponclosure of the relay contact R28a, the now-closed contacts R9b serve toenergize the timer TD4 and relays R34 and R33 as before, but because therelay R42 is energized on the short side heating step of cycle 2, therelay contact R42a allows a selector switch SS6 to be used toimmediately energize the timer TD5 and the relay R17, if so desired, soas to start the control on the potentiometer 225. When this is done, itwill be noted that the relay R17 opens its contacts R17a to permitenergization of the relay R16 which, in turn, closes its contact R16c toenergize the relay R15, thereby removing the potentiometers 222 and 223from the control circuit. Similarly, if desired, a switch SS7 isprovided in series with a contact R42b whereby the short side step ofthe second cycle can be started on the potentiometer 226 by directlyenergized relay R18, the energization of this relay serving to hold thepotentiometers 222 through 225 out of the control circuit by way ofcontacts R18c, R17c, and R16c. Again, the occurrence of a predeterminedmaximum current for this step of the second cycle will produce a currenttrip which will reset the relays of FIG. 6C and advance the side counterrelays to the long side 24-25.

The heating of long side 24-25 during the second or last side heatingcycle is similar to the heating of the long side 22-23 with thefollowing exception. At the end of the heating of short side 23-24 andbefore the heating of long side 24-25, the relay R10 in the side counter254 is energized to open normally closed relay contact R10a and closenormally open relay contact R10b (FIG. 4) to remove the potentiometer165 and replace it with the potentiometer 166. The potentiometer 166 isat a lower setting in order that the long side 24-25 is cooler thanduring the first side welding cycle in preparation for the subsequentdiagonal welding cycle. The advantage of heating the long side 24-25 toa lower temperature than during the first side welding cycle wasdiscussed above.

After the heating of the long side 24-25 and before the heating of theshort side 25-22, the relay R11 in the side counter 254 is energized toopen normally closed relay contact R11a and close normally open relaycontact R11b. The potentiometer 166 is removed from the circuit and thepotentiometer 165 put back in for the heating of short side 25-22.

The heating of short side 25-22 proceeds in accordance with the optionselected for side 24-23 and upon occurrence of the current trip, theside counter relays are shifted and the cycle counter 252 shifts to thefirst diagonal welding cycle. When this occurs, the relay contact R4e isopen and the circuitry of FIG. 6c is removed from the control system sothat the relays and contacts in the automatic sequencer are madeinoperable.

As illustrated in FIG. 2, when the relay R4 is energized at the start ofthe first diagonal welding cycle and the automatic phase sequencer 96 nolonger controls the phase angle of the power regulators 42 and 44. Thepotentiometer 93 of the controller 46 controls the phase angle of thelong side power regulator for the first diagonal welding cycle, thepotentiometer 94 controls the phase angle for the second and thirddiagonal welding cycle; the potentiometer 95 controls the phase anglefor the fourth and fifth diagonal welding cycle.

To start the first diagonal welding cycle, the relay R26 is energized toclose its normally open relay contacts R26b and R26e to energizecontactors C6 and C2, respectively. The contactors C6 and C2 close theircontacts C6a and C2a to apply voltage to electrodes 17 and 19,respectively, to heat sides 25-24-23 and 25-22-23 of the sheet. When thesides are heated to the desired temperature, as indicated by the currenttrip, the relay R27 is energized to close normally open contacts R27a,and R27c, and open contacts R27b and R27d. The contactors C4 and C5 areenergized to close their contacts C4a and C5a. Voltage is applied to theelectrodes 18 and 16 to heat the sides 22-23-24 and 24-25-22 of thesheet.

The above is repeated for the second diagonal welding cycle. At the endof the second diagonal welding cycle, the relay R5 is energized. Theenergization of the relay R5 opens normally closed relay contacts R5a toremove the potentiometer 93 from the controller 46 and closes normallyopen relay contact R5b to put the potentiometer 94 in the controllercircuit. The third diagonal welding cycle proceeds in a similar manneras the first diagonal welding cycle.

After the third diagonal welding cycle, the relay R6 in the cyclecounter is energized to closed normally open relay contact R6b and opennormally closed relay contact R6a. The potentiometer 94 is removed andthe potentiometer 95 is put into the controller circuit 46. The fourthand fifth diagonal welding cycle proceeds in a manner similar to thefirst diagonal welding cycle.

After the fifth diagonal welding cycle, the edges of the glass sheetsare fused to form a glass edge multiple glazed unit.

To accommodate various sides of window unit and to permit compensationfor various characteristics of glass being used, the system is providedwith a number of variables which permit selection of the exact heatingcurrent required for the particular glass and marginal edge beingheated, during the side welding cycles and during the diagonal weldingcycles. Thus, the long sides of glass may be used in accordance with thedifferent pattern than the short sides and in some circumstances it maybe found that selective cycles of heating may be completely skipped. Inaddition to various switches which allow selection for elimination ofpotentiometers and timers which regulate the operation of the system,the potentiometer and timers themselves are adjusted to allow aconsiderable variation of the amount of current applied at any giveninstrument in the heating sequence and to regulate the length of timeduring which the current level is applied.

Although the invention has been described in terms of the preferredembodiment thereof, it will be apparent to those of ordinary skill inthe art that numerous modifications and variations may be made withoutdeparting from the true spirit of the scope thereof as set forth in thefollowing claims.

What is claimed is:
 1. A method of heating marginal edge portions of aglass sheet to a fusing temperature, said marginal edge portions havingcorners and a conductive material thereon, comprising the stepsof:sequentially applying a voltage to an adjacent pair of corners topass an electrical potential along the conductive material to heat themarginal edges to a temperature sufficient for the marginal edges of thesheet to pass; and alternately applying an electrical potential to oneset of diagonally opposed corners of the sheet, and then to another setof diagonally opposed corners of the sheet.
 2. In a method of fusingglass sheets together to form a multiple glazed unit, the glass sheetshaving corners, wherein the method includes the steps of applying aconductive stripe to marginal edge portions of at least one sheet;passing a current through the conductive stripe to heat the marginaledge portions of the sheet to a fusing temperature; and welding themarginal edge portions of the sheets to form the multiple glazed unit,the improvement comprising:sequentially applying a voltage to adjacentcorners of the sheet to sequentially pass an electrical current alongmarginal edge portions of the sheet to heat the glass at the marginaledges to a temperature sufficient to pass a current; and alternatelypassing a current through one set of diagonally opposed corners of thesheet, and then through another set of diagonally opposed corners of thesheet.
 3. The method as set forth in claim 2 wherein said sequentiallyapplying step includes the steps of:passing current along a firstmarginal edge; passing current along a second adjacent marginal edge;passing current along a third marginal edge opposite to the firstmarginal edge; passing current along a fourth marginal edge spaced fromthe second marginal edge; and repeating the above passing steps for apredetermined number of times.
 4. The method as set forth in claim 2wherein said sequentially applying step includes the steps of:passingcurrent along the conductive stripe on a first marginal edge; passingcurrent along the conductive stripe on a second marginal edge; passingcurrent along the conductive stripe on a third marginal edge; passingcurrent along the conductive stripe on a fourth marginal edge; andrepeating the above passing steps for a predetermined number of times.